Correct
When I worked in the dairy/brewery construction industry the highest paid tradesmen on the site were the polishers. They polished the insides of the welded pipe joints to make them all shiny and capable of being sterilized. The welding was done by machine.

To look like this? https://www.picclickimg.com/d/l400/pict/183144828716_/Lambretta-Gp-Polished-Head-Set-Top-Chrome.jpg From the picture you would get similar results by painting it with chrome paint. Answer: You need a source of hi-speed rotation. Bench grinder, die grinder, some cloth polishing whe...

:idea: That is what the bible says... If i put all the bible numbers into a spread sheet they all come out more of less at the same drag coefficient. Except SIL 200 which I assume is the exception that proves the rule. :lol: And the SX150 which I assume is geared low. :?: So if a Lambretta with =/-1...

I am OK with your opinion but I fail to see how drilling out and taping to a larger sized thread is "messing around" We still have to drill out the original hole larger 8.3 for the insert and 5/16 or 7.9 for the larger thread. ( two stages? 7.5mm then 7.9) Surely welding and re-taping is more "messy...